The present invention relates to a power generation system using a fuel cell. More particularly, the present invention relates to a power generation system suitable for use as a power source (driving power supply source) for a load such as an electric car or the like.
In recent years, it is expected that electric cars producing no exhaust gas and generating almost no noise are increasingly substituted for conventional automobiles which have an internal combustion engine requiring gasoline as a fuel mounted thereon year by year. In contrast with the conventional automobile including an internal combustion engine, since each electric car is driven by rotating an electric motor with the aid of a battery serving as a power source to rotate wheels, a most important subject to be solved for putting electric cars in practical use on the commercial basis is concerned with the substantial improvement of properties of each battery serving as a power source for each electric car. In practice, many requests have been raised from users for providing a light battery for an electric car which assures that a large quantity of electrical energy can be stored in the battery so as to enable the electric car to run a sufficiently long distance. However, in case of a hitherto commercially available battery, e.g., a secondary battery such as a lead battery or the like, it has been pointed out as problems that the electric car can run merely by a short distance per each charging compared with a weight of the battery, and moreover, a long time is taken until each charging operation is completed.
In the circumstances as mentioned above, much attention has been lately paid to a fuel cell of the type which can be used in place of the conventional lead battery to serve as a power source for an electric car to enable it to run for a long distance while generating electricity by decomposing a fluid fuel, e.g., a methanol into hydrogen gas in a reforming unit, reforming the thus produced hydrogen gas in the reforming unit, and then allowing the hydrogen gas to react with oxygen in the fuel cell. In other words, in case of the foregoing type of fuel cell, since a raw material used as fuel can be stored in a vehicle in liquid form having a small volume, and moreover, this liquid can be fed to the vehicle in the form of a large quantity of fuel gas (hydrogen gas), a large enough quantity of energy to allow the electric car to run a sufficiently long distance can be stored and reserved in the fuel cell.
To facilitate understanding of the present invention, a typical conventional power generation system using a fuel cell of the foregoing type will be described below with reference to FIG. 1.
FIG. 1 is a systematic diagram which schematically shows essential components of a fuel cell and a secondary cell constituting the power generation system for an electric car. In the drawing, reference numeral 1 designates a fuel cell main body, and reference numeral 2 designates a reforming unit. The fuel cell main body 1 is constructed such that a unit cell is composed of an electrolytic plate 1a, a fuel electrode 1b disposed along one surface of the electrolytic plate 1a and an oxygen electrode 1c disposed along other surface of the electrolytic plate 1a and that a plurality of unit cells each composed in that way are laminated one above another to form a laminated structure. The fuel cell main body 1 includes a cooling member 1d, and when the generation of electric energy is started with the power generation system, a coolant (air) is taken from a coolant inlet port 4 and it is then fed to the cooling member 1d via a coolant preheater 5 so as to cool the fuel main body 1.
On the other hand, a liquid fuel (methanol) is fed to an evaporator 6 from a fuel tank (e.g. a methanol tank) 3a and water is fed from a water tank 3b to the evaporator 6. The liquid fuel and the water are evaporated in the evaporator 6. Subsequently, the evaporated vapor is heated and decomposed by operating a burner 2a in the reforming unit 2, thereby hydrogen gas usable as fuel gas being produced. Subsequently, the hydrogen gas produced in the reforming unit 2 is fed to the fuel electrode 1b in the fuel cell main body 1 and reacts with air (oxygen) taken therein via an air inlet 7 on the oxygen electrode 1c, whereby desired power generation is achieved in the fuel cell main body 1. Since the air after contribution to the power generation contains a large quantity of water vapor, the water is recovered in a water recovering unit 8, and the recovered water is returned to the water tank 3b, and the air is exhausted to the outside via an air exhaust outlet 9. Since power generation in the fuel cell main body 1 in the form of exothermic reaction, it is necessary that a coolant (air) is taken in the power generation system via a coolant inlet 4 and is fed to the cooling member 1d via a coolant preheater 5 so as to cool the fuel cell main body 1 with the coolant. After completion of the cooling operation of the cooling member 1d, the coolant is exhaust to the outside via a coolant exhaust outlet 10.
Thus, the power generation is carried out.
However, the fuel cell for the conventional power generation system has problems as noted below.
One of them is such that since an operating temperature for inducing a power generating function lies at a high level ranging from about 200.degree. to 650.degree. C. which varies depending on the kind of an electrolyte constituting the fuel cell main body 1, it is necessary that the fuel cell main body 1 is heated for activating the fuel cell main body 1, resulting in a long time being taken until the generation of electric energy is started with the fuel cell main body 1. The other problem is such that the power generation system exhibits poor responsibility when a magnitude of the load varies in the course of normal operation of the power generation system as is often the case with an automobile running in the accelerated state or in the decelerated state.
To cope with the foregoing problems, a hybrid type power generation system has been proposed wherein a fuel cell bears a task for allowing an electric car to run by a sufficiently long distance, and a secondary cell bears a task for maintaining electric energy at the starting time or at the time when a magnitude of load varies (see an official gazette of Japanese Patent Publication NO. SHO51-24768 (1976).
Further, it is disclosed that a fuel cell main body is heated up to an elevated temperature by utilizing the energy given by a secondary cell until it reaches a predetermined temperature which makes it possible to generate electric power with the fuel cell main body 1. Specifically, the secondary cell serves as a power source for a coolant preheater at the starting time or the like, and moreover, the coolant serves as a heating medium for heating the fuel cell main body 1. Incidentally, with the hybrid type power generation system including a combination of the fuel cell main body 1 with the secondary cell, when charging of the secondary cell is achieved with the fuel cell main body 1, a charging time can substantially be shortened.
However, in case of the hybrid type power generation system constructed in the above-described manner, the following problems are recognized from the viewpoint of practical use. Specifically, in case that a phosphoric acid is employed as an electrolyte, the power generation system operates at a temperature of about 200.degree. C., and in case that a molten salt is employed as an electrolyte, the power generation system operates at a temperature of about 650.degree. C. In other words, to assure that the power generation system makes it possible to generate electric energy, it is necessary that the fuel cell main body is heated up to a considerably high temperature. For this reason, even though, e.g., a secondary cell additionally disposed for the power generation system is utilized as a heat source, a comparatively long time (e.g., one hour) is taken for heating the fuel cell main body up to an elevated temperature. Therefore, one of the problems is such that the secondary cell is vigorously consumed, and the other one is such that high temperature heat is radiated toward the fuel cell main body 1 and associated components.
On the other hand, in case that the foregoing type of power generation system is employed for an electric car, it is unavoidable that the fuel cell main body 1 and the secondary cell such as a lead battery or the like each supplying electric energy to a predetermined load (e.g., a driving motor, an air conditioner, a lighting device or the like) are closely disposed adjacent to each other due to severe restriction on the space required for disposing or mounting on the electric car. As heat is radiated from the fuel cell main body 1, malfunctions arise with the secondary cell such as a lead battery, a nickel zinc battery, a nickel cadmium battery or the like disposed within the heat radiation range in such a manner that materials constituting the secondary cell are thermally deteriorated due to the heating induced by the heat radiation, the life of charging/discharging cycle is shortened or liquid leakage occurs, resulting in performances of the secondary cell being readily degraded.
In addition, since the power generation system mounted on the electric car receives vibrations and shocks during running of the electric car due to acceleration or deceleration caused when the electric car starts or stops its running, the laminated cell structure constituting the fuel cell main body is readily dislocated from the original position. Further, since the power fed from the fuel cell main body to a load such as a driving motor or the like via a converter usually has an intensity of about 100 amperes or more, the fuel cell main body and the converter are electrically connected to each other via a bus bar 11 made of a plate-shaped metallic material such as nickel or the like having excellent electrical conductivity and a large thickness while extending therebetween as shown in FIG. 2 that is a perspective view of the bus bar 11. Although the bus bar 11 is connected to the fuel cell main body and the converter by tightening bolts and nuts, the connected portions on the bus bar 11 are increasingly loosened during running of the electric car due to vibrations, acceleration or deceleration caused when the electric car starts or stops its running, resulting in the electrical contact resistance arising at the connected portions being undesirably increased. As a high intensity of electric current flows via the bus bar 11, the bus bar 11 is heated and oxidized, causing the electrical resistance to be increased more and more. This leads to the result that the performances of the fuel cell main body 1 are largely and quickly degraded. At any rate, each of the trials hitherto conducted for employing the foregoing type of power generation system as a power source for the electric car by adequately combining advantageous effects of the fuel cell with those of the secondary cell has not been evaluated as effective means at present.